Birthrates of Galactic millisecond pulsars and their low-mass X-ray binary precursors

Abstract

The apparent statistical discrepancy currentlyobserved between the number of Galactic millisecond pulsars and theirlow-mass X-ray binary (LMXB) progenitors is solved if the evolution of arelatively large number of LMXBs is driven by mass transfer sustained byradiation illuminating the companion star. The effective life-time of aradiation-driven LMXB is expected to be of order 10 to the 7th yr, andmuch shorter (by a factor about 10-100) than the typical lifetimesassociated with evolutionary mechanisms which neglect the effect ofradiation from the primary star. The proposed mechanism of evolutionmay be operating for LMXBs with P(orb) not greater than about 10days. This class of X-ray binaries is not expected to be produced bybinary evolution involving the 'prompt' formation of millisecondpulsars after accretion-induced collapse of white dwarf primaries.